A conventional inkjet printer in the art repeatedly performs a recording operation to eject ink from a recording head to a sheet, while moving the recording head in a main scanning direction; and a conveying operation to convey the sheet in a subscanning direction orthogonal to the main scanning direction by means of a conveying device, in order to form images on the sheet. However, due to manufacturing tolerances in the recording head and conveying rollers of the conveying device used to convey the sheet, an incoincidence may occur between the actual conveying length and the theoretical conveying length. In order to improve image quality, a non-uniform conveying operation to convey the sheet by non-uniform distances is suggested.
Japanese Patent Publication 2002-283543 discloses an inkjet printer which performs a non-uniform conveying operation for conveying the sheet by unequal conveying lengths for reducing an occurrence of banding (extraneous lines of ink) every time the recording head moves in the main scanning direction.
This type of inkjet printer further detects the left and right edge positions of the recording medium in order to accurately align the position of the image relative to the recording medium. It is particularly necessary to detect the side edges of the recording medium with high accuracy after the recording medium is conveyed along the subscanning direction, especially for performing marginless printing.
Japanese Patent Publication No. 2004-9529 discloses a recording device for detecting the edges of a recording medium. The recording device is provided with a paper sensor (such as a reflective type photointerrupter) on the carriage on which the recording head is mounted. The sensor irradiates light onto the recording medium while the carriage is scanned, and detects the presence of the recording medium based on the intensity of reflected light.
In order to detect the edges of the recording medium with precision, it is preferable to detect the edges after each conveying operation is completed. However, if the inkjet printer is configured to detect the edges of the recording medium after each conveying operation is completed, the inkjet printer is subject to a greater processing load required for detecting edges of the recording medium.
An object of the invention is to provide an image-forming device which reduces a processing load to obtain high image quality.